Backlights for a liquid crystal display device are divided into two types: direct-lit and edge-lit types, of which a display device with an edge-lit backlight can have a smaller thickness. In an edge-lit backlight, such optical film sheets as a light guide plate, a reflective sheet and a diffusion plate above the light exit surface of the light guide plate are included. A light emitting means emit light rays towards a light incidence surface of the light guide plate, where the light guiding function of the light guide plate enables an area light source to be formed by point light sources. The reflective sheet is arranged at a bottom surface of the light guide plate, for reflecting the light leaked from the bottom surface of the light guide plate so as to enhance the light utilization. For the prior art to fix the reflective sheet, most frequently used is attaching a part of the back side of the reflective sheet 1 to a circuit board 3 of a light bar by using a double-sided adhesive 2 (as shown in FIG. 1), or attaching it to the back plate of the backlight. However, in such methods during the attaching, it is not easy for the reflective sheet 1 to get aligned; in addition, the reflective sheet 1 needs to be torn during repair and maintenance, where since the reflective sheet 1 is of a flexible material, the tearing of the reflective sheet 1 would result in an undesirability such as folding prints in the appearance of the reflective sheet 1, and further, as the reflective sheet 1 has been disassembled, the double-sided adhesive 2 loses its adhesiveness and could not be recycled for second-time uses, which leads to a waste of resources.